Thermal instabilities in cooling flows - The evolution of nearly spherical perturbations

Numerically, in one and two dimensions, the temporal evolution of thermally unstable blobs is presently followed in connection with the problem of mass accretion in cooling flows. The hydrodynamic equations are solved in spherical geometry for an initially homogeneous cooling medium, including thermal conduction. The initial isobaric perturbations are followed in time until self gravity effects, not included in the equations, are thought to become important. In the one-dimensional case, after the linear phase the perturbation evolves on time scales much shorter than the linear ones, and depending on the initial matter density, a cool, dense core of size about 0.001-0.01 times the initial perturbation scale size forms. This grows in size due to continuous accretion from the (hotter) outside gas and may become eventually gravitationally unstable.